I would like to know if there is some way to view the actual CLI commands sent to Saxon when doing XSLT transformations using Oxygen XML GUI.

There are no CLI commands involved when Oxygen runs a Saxon transformation. Since both Oxygen and Saxon are Java-based, Oxygen uses the Saxon Java API for all operations. This also makes it possible to debug with Saxon.

I'm just curious to see the command parameters that Oxygen is using to invoke Saxon. I may want to explore the possibility of a workflow of invoking XSLT transformations from the command line (called from scripts), and I want be able to compare the results to those produced to transformations produced interactively from Oxygen. Does that make sense?

I see, unfortunately this is not the case as there is no CLI command. What Oxygen does via the Java API does not always have a CLI equivalent, so it's difficult to map one to another. Besides, since Saxon transformations are run within the Oxygen Java VM there are various handlers (e.g. protocol handlers) that Oxygen implements and are only available to Saxon within Oxygen's Java environment.

P.S. One of the reasons I asked was I want to find way to invoke transformations for a subset of XML documents.

Say, for instance, I have a set of 2,500 documents in a directory, but I have modified one or two of them. How can I initiate a series of XSLT transformations only on the modified documents, and not the entire directory? I see no way within Oxygen's user interface to select only XML documents modified after a certain date, and run my transformation scenarios on just those.

Say, for instance, I have a set of 2,500 documents in a directory, but I have modified one or two of them. How can I initiate a series of XSLT transformations only on the modified documents, and not the entire directory?

Oxygen doesn't make that distinction for you (for "modified files").I would recommend Eclipse + Oxygen plugin for Eclipse + a version control system (Subversion or git). Eclipse will show you which files are modified locally (if thy are under version control) and maybe you can filter the rest.

But rather than going to the effort of installing Eclipse and learning another IDE, I'd rather work through the command line, where I know I can script operations exactly the way I want. I'm hoping all I will need to do is figure out how to work with Saxon's command line API.